not quite that :
> An editor for iPad, can you be a little bit more specific ?
it is a nice text editor to create nice illustrations, like infographics.
The user can put text, image and shapes and display them to look nice.

> let me synthesize this. You want to make people pay for fonts they can download legally for free here, am I right ?
it is not the paying system that is important but the ability to request and download those fonts automagically.
As it is a commercial product, I want to respect the licence from the original author and give them the fee they are entitled to, like with the "Donate to author" button

Yup, I agree with Myotis. As you can't add fonts to the iPad system, they'll have to be embed to your software. So if you make money out of it, it's clearly a commercial use. I also guess this has to be discussed with each author.

Edit : Furthermore, embedding fonts in a software requires a specific licence most of the time. So my guess is, if you allow the user to write text in your application with a font you/the user have/has downloaded here, it is clearly embedding so... You might get some copyright issues there.

You are right that the fonts must be declared into the app, but they are not obligatory embedded.
I can imagine a process where the user has to download the fonts at runtime, and after licences fee for exemple.

My question was more about API, as I haven't seen automatical integration of dafont.
I think I can also ask webmaster at dafont.com

Well, if a font is used in a software, it "is" embedded. Even if you just use it once and write just one word. At least I can imagine that's what a lawyer would say.

But I don't really get what you mean by "automatical integration" or API.

Edit : Anyway, in my opinion it doesn't change a thing. If you use a font in a software, this requires a different licence - most commercial fonts licences will state this. So, again, if you make money by allowing users to choose fonts, well, this can't be done "automatically", I guess. It would be up to each author to decide if he/she allows the use of his/her font in your software, in if he/she does, what would be the cost.

it is an iPad app, so the user can not simply go to the website and download the font.
I was looking to integrate the search engine of dafont and show the result within my app.
This is usually done via API, where the website can be requested via predefined query and put its answer into xml file.